These teachings relate generally to optical media, and, more particularly, to the formatting of optical media (in an exemplary embodiment, optical tape) used for data or information storage creating a distributed and dispersed pattern of optical marks in such a manner that the reading of this pattern allows for the substantially precise following of the center of each data track.
The recording and reading of data to and from an optical surface such as CD/DVD and other optical media such as optical tape considered in these teachings requires the precise positioning of the write/read laser beam on an identifiable track.
In case of recordable CD/DVD tracks are formed as continuous structure (grooves) as part of the injection molding manufacturing step of the media. These grooves are optically detectable and provide servo information to the actuator that positions the beam on the center of the track and keeps it there.
In the case of optical tape, which is typically hundreds of meters long, the creation of grooves, which typically would run in the longitudinal direction of the tape, is a major technological challenge and hurdle. To do this with great accuracy for several thousands of tracks in parallel leads to a time consuming and uneconomical production of such grooves on tape.
It is therefore a need to provide a different structure that can be applied to the tape in a reliable mode during the manufacturing step of the tape (the so called formatting step) and that contains enough information to provide for the track following function, while allowing enough free space for the recording of user data later on.
It is a further need to be able to perform this formatting operation in a fast one-step process, where the formatting of all tracks is done simultaneously while moving the tape from one end to the other.
There is a need for a structure of “servomarks” that is simple to generate and that satisfies both the need for efficient formatting during tape manufacturing as well as the need for a reliable positioning grid, used during recording or reading of user data, that provides precise tangential position information with respect to the track direction as well as precise longitudinal position information. The tangential information so derived will be used as input for the track servo and the longitudinal information will be used for clock synchronization and identification of data blocks.